Embodiments of the present invention relate to reclaiming substrates in semiconductor fabrication.
In fabricating electronic devices, various materials may be deposited onto a substrate, such as a semiconductor substrate or display, or subsequently etched from the substrate to form features such as interconnect lines. These materials may include metal-containing materials, such as for example, aluminum, copper, tantalum, tungsten, as well as their compounds. Other materials deposited onto substrates include silicon and various oxides and other nonmetallic materials. These materials may be deposited using a variety of techniques including sputtering (also referred to as physical vapor deposition or PVD), chemical vapor deposition (CVD) and thermal growth. In addition to depositing materials, other fabrication processes may be performed including doping semiconductor layers with impurities, diffusion, ion implantation, etching, chemical and mechanical polishing (CMP), cleaning and heat treatments.
In such fabrication processes, test substrates are often used to test whether a fabrication process is operating to specification. For example, to test a copper sputtering process, a test substrate may be placed into a copper sputtering tool and copper sputter deposited onto the test substrate. The test substrate may then be inspected to verify whether or not the resultant deposited copper layer is within specification. If not, the controls to the copper sputtering tool may be adjusted and the tool retested with the same or another test substrate until the desired copper deposition layer is reliably achieved.
With the constant pressure for driving costs down, reclaiming substrates which have been used for testing or monitoring processes, rejected for failing deposition or etch process criteria, or for other reasons, is a good alternative to buying new substrates. It is more cost effective to reclaim the used test substrates rather than simply discard the substrates. The reclamation process typically includes removing all the deposited layers and materials and removing some of the underlying silicon material so that the remaining silicon material of the test substrate is clean and substantially free of added materials or other contaminants. As a consequence, the reclamation process is intended to restore the test substrate to meet the same specifications as a new test substrate except for its thickness. For example, it is often desirable to reclaim test substrates that have contaminants. The reclamation process often has unique requirements when the contaminant comprises metallic species, such as elemental metal or metal compounds. To avoid contamination, it is often preferred that test substrates upon which metallic species have been deposited be reclaimed separately from other test substrates having no metallic deposits or only nonmetal depositions.
With the advancement in technology, more devices are manufactured using copper interconnects and lines, and substrates contaminated with copper-containing species, such as elemental copper or copper compounds, often need to be reclaimed separately from other substrates. The copper from copper-containing substrates can easily contaminate other substrates when they are reclaimed in the same bath used for reclaiming other substrates or even through use of re-circulated polishing slurry. Furthermore, tests for contamination of the substrate surface using ICP-MS (inductively coupled plasma mass spectroscopy) methods do not detect copper which has diffused from the surface into the bulk of the silicon substrate. This can result in shipping to customers, substrates with high levels of copper contamination in the bulk of the substrate. Subsequently, long storage periods or elevated temperatures during transport and warehouse conditions can cause the copper to diffuse from the bulk to the surface where it negatively affects the devices formed on the substrate.
One process of removing metallic contaminants, such as copper, is described in U.S. Pat. No. 6,054,373, Entitled “Methods of and Apparatus for Removing Metallic Impurities Defused in a Semiconductor Substrate”, issued on Apr. 25, 2005, which is incorporated herein by reference in its entirety. This patent describes a process in which a substrate is heated in-situ in an acidic bath of sulfuric acid. However, after removing copper contaminants from a batch of substrates, the resultant chemical bath contains high levels of copper contaminants, which may diffuse into substrates subsequently dipped into the bath. Cross-contamination is a particular problem when a second substrate comprising a low level of surface contamination is treated after a first substrate having a high level of surface contamination, in which case, copper from the first substrate often further contaminates the second substrate.
To segregate the substrates prior to reclamation, used test substrates destined for reclamation are often sorted into one of a few reclamation categories and then stored in cassettes. Notes may be jotted onto each cassette label indicating the particular category (such as “lattice defect type”, “copper”, “metal” or “nonmetal”) to which the test substrates in the cassette is believed to belong. The test substrates may then be transferred to an in-house reclamation service operator or shipped to an outside service provider. The test substrates are often shipped or transferred in bulk, that is, hundreds or thousands at a time. The reclamation service operator, upon receipt of the test substrates, takes note of any notices written on the cassette labels, removes the test substrates from the cassettes, visually inspects the test substrates and sorts them by reclamation category, again, typically the “copper”, “metal” or “nonmetal” categories. The test substrates of each category are then processed using a reclamation process appropriate for that particular category.
One system in which test substrates are reclaimed by reading from a database the process steps performed on each of a plurality of test substrates and selecting a particular reclamation process for each test substrate, is described in U.S. Pat. No. 6,954,722, entitled “TEST SUBSTRATE RECLAMATION METHOD AND APPARATUS”, issued on Oct. 11, 2005, assigned to the assignee of the present application and incorporated by reference in its entirety. For example, where the process steps performed on the test substrates include material deposition; the data read from the database can include data representing the type of material deposited and the thickness of the deposited material in a process step. A reclamation process may then be selected for each test substrate, which is appropriate for that test substrate depending upon the types of materials deposited on the test substrate and the thickness of each deposition. Reclamation processes may be selected based upon other processes performed on the test substrates including ion implantation, CMP, cleaning, thermal treatments and etching and the details concerning those processes. The information identifier for each test substrate, the processes performed on that test substrate and the reclamation process selected for that test substrate, may be stored in a test substrate history database.
In addition, each test substrate for which a reclamation process has been selected may be sorted and placed into a group of test substrates having a common reclamation process assigned to the test substrates of the group. For example, the test substrates may be sorted in an automated system in which an identification code is read from each test substrate by a scanner or other suitable reader, the reclamation process assigned to that test substrate is read from a database and the test substrate is placed by a robot or other automated substrate handlers in a cassette or other bin containing additional test substrates assigned with the same or similar reclamation process.
Also, the bins in which the sorted test substrates are stored may each be labeled with identifying information including basic or detailed information on the reclamation process selected for the test substrates stored in the bin. The information may also include a list of the test substrates stored in each bin. The information identifier for each bin, the test substrates stored in the bin and the reclamation process selected for those test substrates may also be stored in a database for those bins.
The sorted test substrates may be removed from the bins by a reclamation operator in an automated system in which an identification code is read from each test substrate by a suitable reader. The reclamation process assigned to that test substrate can be read from a database supplied to the operator to verify which reclamation process was assigned to each test substrate prior to reclaiming the test substrate.